Volume 37 (2004) Issue 6 Pages 744-750
The feasibility of improving the biodegradability of refractory pollutants in sub- and supercritical water was investigated. Poly vinyl alcohol (PVA) was chosen as a test material to represent high-molecular-weight refractory pollutants. At a temperature of 350°C, BOD increased from 100 mg/L to 3,350 mg/L within 17.4 min, while TOC reduction did not exceed 18%. BOD improvement was calculated based on the change of molecular weight distribution to the range lower than 380 and the decrease of UV absorbance to the range lower than 2.0 × 104 μV in the same molecular weight range. The structural conversion from PVA to biodegradable substances was mainly obtained from hydrolysis and thermal decomposition under sub- and supercritical water conditions. The suitable values of biodegradability (BOD/TOC) for conventional biological treatment methods, 0.78 and 0.79, were obtained in 17.4 min at 350°C and in 7.4 min at 400°C, respectively. The production of biodegradable substances from refractory pollutants by sub- and supercritical water reactions was the most important factor on the viewpoint of the pretreatment of refractory pollutants.